U.S. patent application number 11/592655 was filed with the patent office on 2007-07-05 for coated articles and methods of manufacture thereof.
Invention is credited to Anais E. Espinal, Laura Espinal, Kinga A. Malinger, Lawrence L. Murrell, Steven L. Suib.
Application Number | 20070154639 11/592655 |
Document ID | / |
Family ID | 37888406 |
Filed Date | 2007-07-05 |
United States Patent
Application |
20070154639 |
Kind Code |
A1 |
Malinger; Kinga A. ; et
al. |
July 5, 2007 |
Coated articles and methods of manufacture thereof
Abstract
A method for coating articles includes contacting a substrate
with a mixture comprising a coating composition and a carrier fluid
effective to wet at least a portion of the substrate, and removing
the carrier fluid by microwave heating for a time and at a
temperature effective to produce a coating comprising the coating
composition on at least a portion of substrate. The coated articles
may be useful in a variety of applications including ion, molecule,
and gas separation/filtration; ion-exchanging; semiconductors;
catalysis; and as electrodes, among others.
Inventors: |
Malinger; Kinga A.; (Paris,
FR) ; Espinal; Laura; (Willington, CT) ; Suib;
Steven L.; (Storrs, CT) ; Murrell; Lawrence L.;
(South Plainfield, NJ) ; Espinal; Anais E.;
(Willington, CT) |
Correspondence
Address: |
CANTOR COLBURN, LLP
55 GRIFFIN ROAD SOUTH
BLOOMFIELD
CT
06002
US
|
Family ID: |
37888406 |
Appl. No.: |
11/592655 |
Filed: |
November 3, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60733222 |
Nov 3, 2005 |
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Current U.S.
Class: |
427/256 ;
427/372.2; 427/421.1; 427/429; 427/532 |
Current CPC
Class: |
D21H 17/68 20130101;
C03C 25/42 20130101; C03C 25/16 20130101; C23C 26/00 20130101; D21H
13/40 20130101; C03C 25/10 20130101; B05D 3/029 20130101; C23C 6/00
20130101; D21H 17/67 20130101; D21H 13/50 20130101; D21H 19/02
20130101; B05D 2401/32 20130101; C23C 10/18 20130101; D21H 19/72
20130101; D21H 25/06 20130101; C03C 25/621 20180101; B05D 2203/22
20130101; C03C 25/46 20130101; B05D 2601/20 20130101; C23C 24/08
20130101 |
Class at
Publication: |
427/256 ;
427/532; 427/429; 427/421.1; 427/372.2 |
International
Class: |
B05D 3/00 20060101
B05D003/00; B05D 5/00 20060101 B05D005/00; B05D 3/02 20060101
B05D003/02; B05D 7/00 20060101 B05D007/00; B29C 71/04 20060101
B29C071/04 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
[0002] The United States Government has certain rights in this
invention pursuant to National Science Foundation Grant No.
0304217.
Claims
1. A method for coating articles, the method comprising: contacting
a substrate with a mixture comprising a coating composition and a
carrier fluid effective to wet at least a portion of the substrate;
and removing the carrier fluid by microwave heating for a time and
at a temperature effective to produce a coating comprising the
coating composition on the at least the portion of substrate.
2. The method of claim 1, wherein the contacting comprises dipping
the substrate in the mixture, spraying the substrate with the
mixture, brushing the substrate with the mixture, pouring the
mixture on the substrate, paste casting the mixture on the
substrate, inkjetting the mixture towards the substrate, flowing
the mixture over the substrate in a fluid bed chamber, flowing the
mixture over the substrate in an expanded bed chamber, or a
combination comprising at least one of the foregoing.
3. The method of claim 1, further comprising removing any excess
carrier fluid prior to the microwave heating.
4. The method of claim 3, wherein the removing any excess carrier
fluid prior to the microwave heating comprises allowing gravity to
act on the carrier fluid, agitating the wetted substrate, flowing a
gas over the wetted substrate, contacting the wetted substrate with
an adsorbent material, or a combination comprising at least one of
the foregoing.
5. The method of claim 1, further comprising altering the
microstructure of the coating.
6. The method of claim 5, wherein the altering the microstructure
of the coating comprises sintering, annealing, or calcining the
coating.
7. The method of claim 1, wherein a thickness of the coating is
about 10 nanometers to about 1 millimeter.
8. The method of claim 1, wherein the coating has a less than or
equal to about 10 percent deviation in thickness.
9. The method of claim 1, further comprising depositing an
additional coating on the coating comprising the coating
composition, wherein the additional coating has a same or a
different composition as the coating composition.
10. The method of claim 1, wherein the microwave heating occurs for
about 1 minute to about 6 hours.
11. The method of claim 1, wherein the microwave heating occurs at
about 30 degrees Celsius to about 600 degrees Celsius.
12. The method of claim 1, wherein a frequency of the microwave
heating is about 1 gigaHertz to about 7 gigaHertz.
13. The method of claim 1, wherein the removing the carrier fluid
by microwave heating further comprises thermal heating.
14. The method of claim 1, wherein the coating composition
comprises a metal, alloy, oxide, carbide, form of carbon, nitride,
boride, a composite comprising at least one of the foregoing, or a
combination comprising at least one of the foregoing.
15. The method of claim 1, wherein the removing the carrier fluid
by microwave heating comprises microwave heating in a fluid bed
chamber or an expanded bed chamber while flowing a gas in the fluid
bed chamber or the expanded bed chamber.
16. The method of claim 1, wherein the carrier fluid comprises
deionized water, distilled water, deionized and distilled water,
nitric acid, acetic acid, sulfuric acid, phosphoric acid,
hydrofluoric acid, a hydroxide of Na, K, or NH.sub.4, an alcohol, a
polyol, a ketone, or a combination comprising at least one of the
foregoing carrier fluids.
17. The method of claim 1, wherein the substrate comprises a metal,
alloy, ceramic, glass, polymer, fluorinated polymer, quartz,
sapphire, wood, paper, carbon, or a combination comprising at least
one of the foregoing.
18. A coated article produced by the method of claim 1.
19. A method of coating articles, the method comprising: contacting
a three-dimensional network of fibers with a mixture comprising a
coating composition and a carrier fluid effective to wet at least a
portion of the fibers, removing the carrier fluid by microwave
heating for a time and at a temperature effective to produce a
coating comprising the coating composition on the at least the
portion of fibers.
20. The method of claim 19, wherein the contacting comprises
dipping the fibers in the mixture, spraying the fibers with the
mixture, brushing the fibers with the mixture, pouring the mixture
on the fibers, inkjetting the mixture on the fibers, paste casting
the mixture on the fibers, flowing the mixture through the fibers
in a fluid bed chamber, flowing the mixture through the fibers in
an expanded bed chamber, or a combination comprising at least one
of the foregoing.
21. The method of claim 19, further comprising allowing gravity to
act on the carrier fluid, agitating the wetted substrate, flowing a
gas over the wetted substrate, contacting the wetted substrate with
an adsorbent material, or a combination comprising at least one of
the foregoing, effective to remove any excess carrier fluid from
the fibers prior to the microwave heating.
22. The method of claim 19, further comprising sintering,
annealing, or calcining the coating.
23. The method of claim 19, wherein a thickness of the coating is
about 10 nanometers to about 1 millimeter.
24. The method of claim 19, further comprising producing an
additional coating composition on the coating, wherein the
additional coating has a same or a different composition as the
coating composition.
25. The method of claim 19, wherein the removing the carrier fluid
by microwave heating comprises microwave heating in a fluid bed
chamber or an expanded bed chamber while flowing a gas in the fluid
bed chamber or the expanded bed chamber.
26. The method of claim 19, wherein the three-dimensional network
of fibers comprise form a non-woven paper.
27. The method of claim 19, wherein the fibers of the
three-dimensional network of fibers have an average diameter of
about 5 micrometers to about 15 micrometers, and an average basis
weight of about 18 grams per square meter to about 300 grams per
square meter.
28. The method of claim 19, wherein the three-dimensional network
of fibers comprise silica fibers, silica-like fibers, carbon
fibers, or a combination comprising at least one of the
foregoing.
29. A coated three-dimensional network of fibers produced by the
method of claim 19.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims the benefit of U.S.
Provisional Patent Application No. 60/733,222, which was filed on
Nov. 3, 2005, and is herein incorporated by reference in its
entirety.
BACKGROUND
[0003] Coatings play a prominent role in the manufacture and
performance of many devices. They are used to tailor the surfaces
of a substrate, for example, to provide a different appearance
(e.g., color, shape, and/or dimension), control friction and wear,
inhibit corrosion, and/or change a physical property (e.g.,
adsorption, conductivity, or the like) of a substrate. A variety of
techniques have been developed to provide coated articles.
[0004] Two frequently used methods of applying coatings to a
substrate include dipping a substrate into, or spraying a substrate
with, a solid-liquid mixture containing the coating material,
followed by removal of the liquid. Unfortunately, it may be
difficult, using these techniques, to produce uniform coatings in
which the thickness of the coating at the corners or edges of a
three-dimensional substrate is substantially the same as the
coating thickness at other portions of the substrate. This problem
is exacerbated when the substrate is textured and/or porous. The
non-uniformity in the coating arises primarily during removal of
the liquid, which has been sprayed on the substrate or into which
the substrate has been dipped.
[0005] To overcome the difficulties in obtaining uniform coatings
on three-dimensional substrates, liquidless techniques have been
developed. For example, powder coating is based on dipping a
substrate into a bed of an electrostatically charged powder, or on
spraying an electrostatically charged powder onto the substrate.
While these methods may produce more uniform coatings, additional
complexities (e.g., extensive substrate surface and/or coating
powder preparation steps) may be introduced that do not exist for
processes using liquids.
[0006] There accordingly remains a need in the art for new methods
of preparing coated articles. It would be particularly advantageous
if these methods provided the desired uniform coatings on
three-dimensional substrates, such as those associated with powder
coating, without simultaneously requiring additional and/or more
complex processing steps.
SUMMARY
[0007] A method for coating articles includes contacting a
substrate with a mixture comprising a coating composition and a
carrier fluid effective to wet at least a portion of the substrate,
and removing the carrier fluid by microwave heating for a time and
at a temperature effective to produce a coating comprising the
coating composition on at least a portion of substrate.
[0008] In another embodiment, the method includes contacting a
three-dimensional network of fibers with a mixture comprising an
oxide composition and a carrier fluid effective to wet at least a
portion of the fibers and removing the carrier fluid by microwave
heating for a time and at a temperature effective to produce an
oxide coating on at least a portion of the fibers.
[0009] Other embodiments include coated articles made by above
methods.
[0010] The above described and other features are exemplified by
the following figures and detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Referring now to the Figures, which are exemplary
embodiments, and wherein the like elements are numbered alike:
[0012] FIG. 1 is a representative color photographic image of a
convection dried sample of quartz-like fibers within a non-woven
paper which was dipped in a 30 weight percent (wt %) suspension of
silica;
[0013] FIG. 2 is a representative color photographic image of a
microwave dried sample of quartz-like fibers within a non-woven
paper which was dipped in a 30 wt % suspension of silica;
[0014] FIG. 3 illustrates representative scanning electron
micrographs of coatings produced from microwave drying of fibers
within a non-woven paper which have been dipped in a 5 wt % silica
colloidal suspension, shown at (a) 3,000 and (b) 10,000 times
magnification;
[0015] FIG. 4 illustrates representative scanning electron
micrographs of coatings produced from microwave drying of fibers
within a non-woven paper which have been dipped in a 10 wt % silica
colloidal suspension, shown at (a) and (b) 5,000 times
magnification;
[0016] FIG. 5 illustrates representative scanning electron
micrographs of coatings produced from microwave drying of fibers
within a non-woven paper that have been dipped in a 20 wt % silica
colloidal suspension, shown at (a) 3,000 and (b) 5,000 times
magnification;
[0017] FIG. 6 illustrates representative scanning electron
micrographs of coatings produced from microwave drying of (using a
variable frequency microwave furnace) of fibers within a non-woven
paper that have been dipped in a 20 wt % silica colloidal
suspension, shown at (a) and (b) 5,000 times magnification;
[0018] FIG. 7 illustrates representative scanning electron
micrographs of coatings resulting from sequentially microwave
drying of fibers within a non-woven paper that have been dipped in
a 5% silica colloidal suspension, shown at (a) 10,000, (b) 10,000,
(c) 5,000, and (d) 5,000 times magnification;
[0019] FIG. 8 illustrates representative scanning electron
micrographs of coatings produced from microwave drying of fibers
within a non-woven paper that have been dipped in a 10 wt % alumina
colloidal suspension, shown at (a) 3,000 and (b) 10,000 times
magnification;
[0020] FIG. 9 illustrates representative scanning electron
micrographs of coatings produced from microwave drying of fibers
within a non-woven paper that have been dipped in a 10 wt % ceria
colloidal suspension, shown at (a) 5,000 and (b) 50,000 times
magnification;
[0021] FIG. 10 illustrates representative scanning electron
micrographs of coatings produced from microwave drying of fibers
within a non-woven paper that have been dipped in a 10 wt %
zirconia colloidal suspension, shown at (a) 3,000 and (b) 5,000
times magnification;
[0022] FIG. 11 illustrates representative optical images of
coatings produced by (a) room temperature evaporating, (b)
convection heating, and (c) microwave heating of fibers within a
non-woven paper that have been dipped in a suspension having 9.5 wt
% activated charcoal and 0.5 wt % silica; and
[0023] FIG. 12 illustrates representative scanning electron
micrographs of (a) an uncoated quartz-like fiber within a non-woven
paper, and coatings produced by (b) room temperature evaporating,
(c) convection heating, and (d) microwave heating of fibers within
a non-woven paper that have been dipped in a suspension having 9.5
wt % activated charcoal and 0.5 wt % silica.
DETAILED DESCRIPTION
[0024] Disclosed herein are methods of manufacturing coated
articles. The methods generally comprise contacting a substrate
with a mixture comprising a coating composition and a carrier fluid
effective to wet at least a portion of the substrate, and removing
the carrier fluid by microwave heating for a time and at a
temperature effective to produce a coating comprising the coating
composition on at least the portion of substrate. In an
advantageous feature, the coated articles produced by the methods
disclosed herein can have uniform coatings in which the thickness
of the coating at the corners or edges of the substrate is
substantially the same as the coating thickness at other portions
of the substrate.
[0025] The term "wet" is used herein in its broadest sense to
indicate any maintained contact between the mixture and any surface
of the substrate, and includes discrete beading of the mixture on
portions of the substrate's surface as well as a continuous film of
the mixture distributed over the surface of the substrate. The term
"substrate" is used herein for convenience to generally refer to
the article having the coating disposed thereon, and includes
materials having irregular shapes such as flakes, fibers (woven or
non-woven), honeycomb materials, as well as regular shapes such as
for example monoliths, spheres, and films.
[0026] Also as used herein, the terms "first," "second," and the
like do not denote any order or importance, but rather are used to
distinguish one element from another, and the terms "the", "a" and
"an" do not denote a limitation of quantity, but rather denote the
presence of at least one of the referenced item. Furthermore, all
ranges reciting the same quantity or physical property are
inclusive of the recited endpoints and independently combinable.
The modifier "about" used in connection with a quantity is
inclusive of the stated value and has the meaning dictated by the
context or includes the degree of error associated with measurement
of the particular quantity.
[0027] The mixture comprising the coating composition and the
carrier fluid may be a suspension (e.g., an emulsion, dispersion,
slurry, or the like), colloid (e.g., fine particle containing
suspensions, sols, or the like), or a solution, or a combination
comprising at least one of the foregoing.
[0028] Any composition may be used for the coating composition,
provided that it is in solid form within the above-described
mixture. Suitable coating compositions include a metal, an alloy,
an oxide, a carbide, a form of carbon, a nitride, a boride, a
composite comprising at least one of the foregoing, or a
combination comprising at least one of the foregoing. Exemplary
oxides include Al.sub.2O.sub.3, CeO.sub.2, Cr.sub.2O.sub.3,
ZrO.sub.2, SiO.sub.2, Y.sub.2O.sub.3, La.sub.2O.sub.3, TiO.sub.2,
SnO.sub.2, and the like, and combinations comprising at least one
of the foregoing. Exemplary carbides include Cr.sub.3C.sub.2, WC,
TiC, ZrC, SiC, B.sub.4C, and the like, and combinations comprising
at least one of the foregoing. Exemplary forms of carbon include
graphite, diamond, charcoal, activated charcoal, carbon black, and
the like, and combinations comprising at least one of the
foregoing. Exemplary nitrides include BN, TiN, ZrN, HfN,
Si.sub.3N.sub.4, AlN, and the like, and combinations comprising at
least one of the foregoing. Exemplary borides include TiB.sub.2,
ZrB.sub.2, LaB, LaB.sub.6, W.sub.2B.sub.2, and the like, and
combinations comprising at least one of the foregoing.
[0029] When the mixture is a suspension, an average longest
dimension of a coating composition particle is greater than about 1
micrometer (.mu.m). Desirably, the average longest dimension of the
coating composition particle in a suspension is less than about 6
.mu.m. When the mixture is a colloid, the average longest dimension
of a coating composition particle is greater than or equal to about
1 nanometer (nm) and less then or equal to about 1 .mu.m. If the
mixture is a solution, then the coating composition will be at
least partially dissolved in the carrier liquid with no restriction
on the particle size of any particles not dissolved.
[0030] The carrier fluid used in the mixture may comprise any
aqueous or organic compound, or mixture thereof, that is a liquid
at the contacting temperature, provided that this fluid does not
adversely affect the coating composition and/or the substrate.
Suitable carrier fluids include water, such as deionized water
(DI--H.sub.2O), distilled water, or deionized distilled water
(DDW); acids, such as nitric acid, acetic acid, sulfuric acid,
phosphoric acid, hydrofluoric acid, and the like; bases, such as
hydroxides of Na, K, NH.sub.4, and the like; alcohols; polyols;
ketones; and the like; and a combination comprising at least one of
the foregoing.
[0031] The mixture may further contain other components known in
the art. For example, the mixture may comprise stabilizers, pH
regulators, viscosity modifiers, wetting agents, water soluble
polymers, and/or other chemical agents that may promote wetting of
the substrate, inhibit settling of the coating composition within
the mixture and/or aid in attachment of the coating to the
substrate.
[0032] In an exemplary embodiment, the mixture is a colloid
comprising oxide particles having an average longest dimension of
about 1 nm to about 0.6 .mu.m in water and/or ethylene glycol. In
another exemplary embodiment, the mixture comprises dry or wet
milled particles mixed with a colloid, which serves as a binder for
the milled particles to bind to the surface of the substrate.
[0033] The substrate may be any solid material with a surface on
which the coating will deposit, provided that the substrate is not
adversely affected by the microwaves and/or any of the mixture
components. Suitable substrates include metals, alloys, ceramics,
glass, organic polymers, fluorinated polymers, quartz, sapphire,
wood, paper, carbon, and the like. Suitable metals include
transition group metals, rare earth metals including lanthanides
and actinides, alkali metals, alkaline earth metals, main group
metals, and combinations comprising at least one of the foregoing
metals. Suitable ceramics include the oxides, carbides, nitrides
and borides described above, as well as aluminosilicates, clays,
and the like. Suitable fluorinated polymers include
tetrafluoroethylene (TFE), poly(tetrafluoroethylene) (PTFE),
fluoroethylene-propylene (FEP), and the like.
[0034] As stated above, the substrate is not intended to be limited
to a particular size, shape, and/or texture. The size, shape and/or
texture of the substrate do not appear to be critical to the
ability of the coating to be formed.
[0035] In a specific embodiment, the substrate is a ceramic
honeycomb structure. In another specific embodiment, the substrate
is a three-dimensional network of fibers within a non-woven paper,
wherein the fibers have an average diameter of about 5 to about 15
.mu.m, and an average basis weight of about 18 to about 300 grams
per square meter (gsm). The fibers within the paper may have an
ordered orientation or may be randomly oriented with respect to
each other. The three-dimensional network of fibers may be held
intact by a polymeric binder positioned at the intersections of the
fibers. Exemplary fiber materials include silica (e.g., quartz)
fibers, or silica-like (e.g., quartz-like) fibers, carbon fibers,
and the like.
[0036] The mixture may be contacted with the substrate in various
ways. These include dipping or immersing the substrate in the
mixture, spraying the substrate with the mixture, brushing the
substrate with the mixture, pouring the mixture on the substrate,
paste casting, inkjetting the mixture towards the substrate, or the
like, or a combination comprising at least one of the foregoing.
The particular method of contacting the substrate with the mixture
will be selected based on the properties of the substrate and/or
the concentration of the coating composition within the mixture.
For example, for a highly porous substrate, it may be advantageous
to immerse the substrate in the mixture and/or pour the mixture on
the substrate to maximize the amount of the overall surface area of
the substrate that the mixture can contact. Alternatively, if only
a portion of the substrate is to be coated, spraying, brushing,
paste casting, and/or inkjetting the portion of the substrate with
the mixture may be most desirable.
[0037] Once the substrate has been sufficiently wetted with the
mixture, it may be desirable to remove excess carrier fluid from
the substrate. This can be performed by simply allowing the force
of gravity to act on the carrier fluid, agitating (e.g., shaking)
the wetted substrate, flowing a gas (e.g., air) over the wetted
substrate, contacting the wetted substrate with an adsorbent
material (e.g., sponge, towel, tissue, and the like), or the like,
or a combination comprising at least one of the foregoing. Without
being bound by theory, it is believed that performing this optional
step minimizes the opportunity for so-called build up of the
coating composition at a specific location on the surface of the
substrate to occur, and thereby increases the likelihood that a
more uniform distribution of the coating composition over the
entire substrate can be achieved.
[0038] After the contacting step or optional excess carrier fluid
removal step, the wetted substrate is exposed to microwave
irradiation so that the remainder of the carrier fluid can be
removed and the coating can be formed.
[0039] The microwave heating process can be performed with
different types of microwave systems, all of which can effectively
localize microwave power. A microwave system generally comprises a
sample chamber in communication with a microwave source. One type
of microwave system is a single pass, traveling wave applicator,
where microwave energy propagates down the length of a waveguide,
where the maximum field and power is concentrated at the center of
the waveguide where the sample is located. A second type of system
is a standing wave system where the microwaves are introduced into
a tuned chamber, which concentrates the microwave energy at the
location of the sample. A third system is a beam system, where
microwave energy is focused directly onto the sample. Suitable
microwave sources include, but are not limited to, a magnetron and
a gyrotron.
[0040] Suitable frequencies include, but are not limited to about 1
gigaHertz (GHz) to about 7 GHz. Suitable microwave powers may be up
to, but not limited to, about 1300 Watts (W). The microwave heating
process may be carried out at any temperature provided that the
temperature does not adversely affect (e.g., melt, decompose, or
the like) the substrate and/or mixture, and does not cause a side
reaction between the substrate and any of the components of the
mixture. Suitable temperatures may be about 30 degrees Celsius
(.degree. C.) to about 600.degree. C. The duration of the microwave
heating will depend upon several factors including the microwave
energy and frequency, as well as the carrier fluid to be removed.
In one embodiment, microwaving can be performed for a time of about
1 minute to about 6 hours. More specifically, microwave heating can
be performed for about 10 minutes to about 1 hour.
[0041] Without being bound by theory, in conventional heating
methods, relying solely on convection, thermal energy is absorbed
on the surface of an object to be heated and then is transferred
towards the interior of the object via thermal conductivity.
Because energy transfer is occurring that is localized at the
surface, the process can be quite slow. With microwave heating,
owing to deep penetration by the microwaves, energy is absorbed by
the object to be heated as a whole and then converted to heat via
dielectric loss mechanisms and/or eddy current losses (if the
object is electrically conductive). Because there is effective
energy conversion, the process can be quite rapid. Furthermore,
with microwave irradiation, the heating is more uniform and less
localized, which, with respect to removing the carrier fluid,
results in decreased migration of the coating composition during
the drying process. This, in turn, results in coatings that may be
more uniform and have fewer or no bare spots.
[0042] In an exemplary embodiment, the microwave heating is
performed while the wetted substrate is in a fluid bed chamber or
an expanded bed chamber. For example, microfiber particles can be
formed from a three-dimensional network of fiber paper that has
been shaped to the desired size, such as by water jet cutting,
laser cutting, die cast cutting, or the like. Desirably, the
particles are shaped to be spherical or substantially spherical,
with a narrow distribution of the particle size, to achieve the
appropriate volume expansion conditions. In a fluidized bed, the
particles may have an average diameter of about 30 .mu.m to about 1
millimeter (mm); while, in an expanded bed, the particles may have
an average diameter of about 10 .mu.m to about 5 mm. A plurality of
microfiber particles can be placed in a fluid bed or expanded bed
chamber and contacted with the mixture comprising the coating
composition by flowing the mixture through the chamber, or can be
contacted with the mixture comprising the coating composition as
described above and subsequently placed in the fluid bed or
expanded bed chamber. Once the plurality of wetted microfiber
particles has been disposed in the fluid bed or expanded bed
chamber, the microwave heating step can be performed while a gas
flows through the bed to achieve the desired volume expansion. The
gas can be a reducing or oxidizing gas if the desired final coating
composition is slightly different than what is included in the
mixture, or the gas can be an inert gas. Further, the gas can be
heated or dried to facilitate removing the carrier fluid of the
mixture from the substrate.
[0043] In one embodiment, both microwave heating and thermal
heating can be used to remove the carrier fluid. In this manner,
the overall heating time can be reduced. The thermal heating may be
achieved by contacting the wetted substrate with a heated gas while
it is contained inside the microwave system. The particular gas may
have any composition provided that the gas is not involved in a
side reaction with the substrate, any of the components of the
mixture, and/or the microwave irradiation. Exemplary gases include
air, nitrogen, any of the inert gases, or the like. Desirably, the
gas is introduced into the microwave system with a sufficiently low
pressure so as to prevent coating composition particles from being
removed from the substrate.
[0044] Once the coating has been formed, the coating may undergo an
optional sintering, annealing, or calcining step (depending on the
particular composition of coating that has been formed). These
microstructure altering or developing heat treatments can be
performed in any environment (e.g., air, hydrogen, nitrogen,
oxygen, or the like), the temperature and duration of which are
dependent on the particular composition and extent of
microstructure alteration or development necessary.
[0045] The thickness of the coating may be controlled by the
dimension of the substrate, the extent of the contacting, and/or
the concentration of the coating composition in the mixture. The
average thickness of the coating may be about 10 nm to about 1
millimeter (mm).
[0046] As previously mentioned, the coatings produced by the
methods disclosed herein may be more uniform than those of the
prior art. For example, it is possible to produce coatings which
have less than or equal to about 10% deviation in thickness over
essentially the entire coating. It is also possible to produce
coatings that have less than or equal to about 5% deviation in
thickness over essentially the entire coating.
[0047] Those skilled in the art in view of this disclosure should
recognize that multiple, sequential coatings can advantageously be
deposited onto a single substrate by simply repeating the coating
process using the same or a different coating composition. If the
same coating composition is used, then repeating the coating
process serves to control (by increasing) the thickness of the
coating. However, if a different coating composition is used, then
repeating the coating process results in a layered article. In
certain cases it may be useful to perform a microstructure altering
or developing heat treatment on the coating after one or more of
the coating and microwave treatment steps at a high temperature in
order to obtain the most uniform final coated structure. For
example, in one embodiment, a first coating composition can be
deposited and may serve as a support for a second coating
composition which may be a catalytically active material. In this
manner, a heterogeneous catalyst can be formed on a substrate
having a selected shape or structure for a desired application. In
another embodiment, the second coating composition can be
selectively deposited on only a portion of the coated substrate by
simply contacting only that portion of the coated substrate with
the second mixture. For example, a uniform coating within a fiber
substrate could be deposited, and then a subsequent coating could
be deposited only at the surface of the fiber substrate.
[0048] The coatings and coated articles are useful in a variety of
applications including, but not limited to, ion, molecule, and gas
separation/filtration; ion-exchanging; semiconductors; catalysis;
and as electrodes, among others.
[0049] The disclosure is further illustrated by the following
non-limiting examples.
EXAMPLE 1
Comparison Between Convection and Microwave Dried Silica Coated
Quartz-like Fiber Paper
[0050] Quartz-like fiber non-woven paper (obtained under the trade
name CRANEGLAS 500), having a thickness of about 1/8 inch and a
weight of about 0.1 grams (g) was used as the substrate. Postage
stamp sized pieces of the quartz-like non-woven fiber paper were
independently dipped into a 20 weight percent (wt %) and 30 wt %
colloidal suspension of silica (LUDOX), based on the total weight
of the suspension. Subsequently, the samples were contacted with
tissue paper and/or a glass surface to remove any excess liquid.
The weight of the samples after removing the excess liquid was
about 1.2 g.
[0051] One sample of each type (i.e., those dipped in the 20 wt %
suspension and those dipped in the 30 wt % suspension) was placed
vertically in separate Pyrex beakers, which were inserted into a
convection furnace. The samples were dried for about 1 hour at
about 120.degree. C.
[0052] Alternatively, one sample of each type was placed in
separate Teflon containers, which were inserted into a constant
frequency microwave furnace operating at about 2.45 GHz. The
samples were dried for about 30 minutes at about 120.degree. C.
[0053] Finally, all samples were calcined at about 600.degree. C.
for about 6 hours. The final weight of the samples was about 0.4
g.
[0054] The convection dried samples had uneven distribution of the
oxide on the quartz fibers. Specifically, a majority of the
SiO.sub.2 was found on the outside edges or surfaces of the paper,
while, in some regions, there was no coating whatsoever. In
addition, some of the SiO.sub.2 did not coat the fibers, but
instead was observed to be held in place between various fibers.
FIG. 1, which is a representative photographic image of a
convection dried quartz fiber sample dipped in the 30 wt %
suspension, clearly illustrates these characteristics.
[0055] In stark contrast, a substantially uniform coating was
observed throughout the paper for the microwave dried samples. A
representative photographic image of a microwave dried quartz fiber
sample dipped in the 30 wt % suspension is shown in FIG. 2. As
evidenced, the SiO.sub.2 coating showed no preference for the edges
of the paper.
EXAMPLE 2
Quartz-like Fiber Paper Dipped in Silica Suspensions of Varying
Concentrations
[0056] In this example, the effect of using silica suspensions
having different concentrations of SiO.sub.2 therein was studied.
Microwave dried samples of quartz-like fiber papers dipped in
silica suspensions were prepared according to Example 1, except
that the fiber paper was about 1/16 inch thick. The concentration
levels of silica in suspension used were 5 wt %, 10 wt %, and 20 wt
%.
[0057] High resolution field emission scanning electron microscopy
(SEM) indicated that the thickness of the individually coated
fibers increased with the concentration of SiO.sub.2 in the
suspension. FIGS. 3 through 5 are representative SEM images of
coatings resulting from microwave drying of fibers dipped in the 5
wt %, 10 wt %, and 20 wt % SiO.sub.2 suspensions, respectively. The
coating fractures shown in the micrographs throughout this
disclosure are a result of mechanical processing of the sample
during preparation for microscopy. However, from these fractures,
it is possible to measure the thickness of the coating deposited on
the particular fiber shown in each micrograph. For example, in the
SEM image shown in FIGS. 3 (b), 4 (b), and 5 (b), the thickness of
the coating deposited on the fibers shown are about 500 nanometers
(nm), about 1 micrometer (.mu.m), and about 1.25 .mu.m,
respectively.
EXAMPLE 3
Variable Frequency Microwave Furnace Dried Silica Coated
Quartz-like Fiber Paper
[0058] In this example, samples were prepared according to Example
1, except that a variable frequency microwave furnace was used to
dry the samples. A center frequency of about 4 GHz was used while
varying the power from about 33 to about 99 W with a sweep time of
about 10 seconds (s) to heat the samples at about 120.degree. C.
for about 30 minutes.
[0059] Similar to those coatings obtained using a continuous
frequency microwave furnace, the coatings obtained using a variably
frequency microwave furnace were substantially uniform and markedly
superior to those obtained using a convection furnace. FIG. 6
illustrates representative SEM images of coatings resulting from
microwave drying (using a variable frequency microwave furnace)
fiber papers dipped in a 20 wt % SiO.sub.2 suspension.
EXAMPLE 4
Sequential Coating of Quartz-like Fiber Paper
[0060] In this example, samples were sequentially coated by
repeating the procedure described in Example 1 (i.e., dipping,
removing excess liquid, microwave drying, and calcining) for a
particular piece of quartz-like fiber paper. Each repetition of
this procedure resulted in a coating of increased thickness.
[0061] FIG. 7 (a) is a representative SEM image showing a coating
resulting from microwave drying (using a constant frequency
microwave furnace) a sample dipped in a 5 wt % SiO.sub.2
suspension. FIGS. 7 (b)-(d), respectively, illustrate
representative SEM images of coatings resulting from first, second,
and third repetitions of the procedure described in Example 1.
EXAMPLE 5
Alumina Coated Quartz-like Fiber Paper
[0062] In this example, samples were prepared according to Example
1, except that a 10 wt % colloidal suspension of alumina (NYACOL
AL20DW) was used to produce Al.sub.2O.sub.3 coated quartz-like
fiber paper samples.
[0063] FIG. 8 illustrates representative SEM images of coatings
resulting from microwave drying (using a constant frequency
microwave furnace) of fibers within fiber papers dipped in the 10
wt % alumina suspension. The thickness of the coating deposited on
the fibers shown in FIG. 8 (b) is about 500 nm.
[0064] Energy dispersive X-ray spectroscopy (EDX) revealed the
cation content of the coated quartz-like fiber paper to be
31.01.+-.1.41% Al and 68.99.+-.1.41% Si.
EXAMPLE 6
Ceria Coated Quartz-like Fiber Paper
[0065] In this example, samples were prepared according to Example
1, except that a 10 wt % colloidal suspension of ceria (NYACOL) was
used to produce CeO.sub.2 coated quartz-like fiber paper.
[0066] FIG. 9 illustrates representative SEM images of coatings
resulting from microwave drying (using a constant frequency
microwave furnace) of fiber papers dipped in the 10 wt % ceria
suspension. The thickness of the coating deposited on the fibers
shown in FIG. 9 (b) is about 400 nm.
[0067] EDX revealed the cation content of the coated quartz-like
fiber paper to be 58.74.+-.1.82% Ce and 41.26.+-.1.82% Si.
EXAMPLE 7
Zirconia Coated Quartz-like Fiber Paper
[0068] In this example, samples were prepared according to Example
1, except that a 10 wt % colloidal suspension of zirconia (NYACOL)
was used to produce ZrO.sub.2 coated quartz-like fiber paper.
[0069] FIG. 10 illustrates representative SEM images of coatings
resulting from microwave drying (using a constant frequency
microwave furnace) fiber papers dipped in the 10 wt % zirconia
suspension. The thickness of the coating deposited on the fibers
shown in FIG. 10 (b) is about 310 nm.
[0070] EDX revealed the cation content of the coated quartz fiber
paper to be 41.01.+-.4.97% Zr and 58.99.+-.4.97% Si.
EXAMPLE 8
Comparison Between Drying Methods for Activated Charcoal Coated on
Quartz-like Fiber Paper
[0071] In this example, activated charcoal was coated on
quartz-like fiber paper using a silica binder to facilitate
coating. Three different drying methods were utilized so that the
coating quality could be compared.
[0072] Samples were prepared according to Example 1, except that a
slurry having 9.5 wt % activated charcoal and 0.5 wt % of colloidal
silica (LUDOX) was used to produce the activated charcoal coated
quartz-like fiber paper. Furthermore, instead of contacting the
samples with tissue paper and/or glass to remove excess liquid, the
samples were gently shaken.
[0073] The three drying methods included room temperature (i.e.,
about 23 to about 28.degree. C.) evaporation of the carrier fluid
for about 48 hours in a hood, heating in a convection furnace for
about 50 minutes at about 120.degree. C., and microwave heating for
about 30 minutes at about 120.degree. C. The samples dried in the
hood were suspended using polyester fishing line. A watch glass was
employed to hold the samples inside the convection furnace.
Finally, polyester fishing line was used to hold the samples
vertically, and to prevent the samples from moving, while being
suspended over a non-microwave absorbent tray within the microwave
furnace.
[0074] FIG. 11 illustrates representative optical images of the (a)
room temperature dried, (b) convection heated, and (c) microwave
heated coatings. Furthermore, FIG. 12 illustrates representative
field emission SEM images of (a) an uncoated quartz-like fiber
within a non-woven paper, and a (b) room temperature dried; (c)
convection heated, and (d) microwave heated fiber, within a
non-woven paper, of the coating. From FIGS. 11 and 12, it is
apparent that the microwave heated samples exhibited a more
uniformly distributed coating of the activated charcoal than did
the non-microwave heated samples.
[0075] The coatings produced by microwave heating were more stable
than the other two types of coatings, as evidenced by the flaking
of a fine black powder from the other two samples after the drying
step. Therefore, it is believed that the microwave heating may have
facilitated the binding of the activated charcoal to the
quartz-like fibers via the silica acting as a binder within the
suspension.
[0076] While the invention has been described with reference to
exemplary embodiments, it will be understood by those skilled in
the art that various changes may be made and equivalents may be
substituted for elements thereof without departing from the scope
of the invention. In addition, many modifications may be made to
adapt a particular situation or material to the teachings of the
invention without departing from the essential scope thereof.
Therefore, it is intended that the invention not be limited to the
particular embodiment disclosed as the best mode contemplated for
carrying out this invention, but that the invention will include
all embodiments falling within the scope of the appended
claims.
* * * * *